1) Let Shutterstock or the actual owner of the misused photos police themselves. It good to contact the owners and make them aware of the issue, but its not your property or decision to make.
2) Your message on their website is a direct attack and you should expect people to react badly and aggressively. Do not say anything online that you would not say in person to their face.
“Never argue with a fool, onlookers may not be able to tell the difference.”
― Mark Twain
3) Missused photos are best reported on a website such as Photo Stealers http://stopstealingphotos.com/ This will keep it less personal and reduce the backlash.
4) The multiple false and harassing reviews should be handled by a real lawyer.
5) The OP seems highly concerned with the actions of other people in a situation that she was not originally involved. Almost all successful people focus their positive energy on their own progress, and don't let themselves get stuck in the mud of drama of others. I hope the OP would strongly rethink her actions here and try to avoid wasting so much time and inciting so much negativity to her business.